The invention relates to a method for feeding flat items for separation by suction of material input into a distributing unit by using a feeding device, preferably comprising a separating blade and a conveyor belt arranged underneath.
The items are fed to the system for separation by suction by way of the separating blade and the conveyor belt arranged underneath. If the pressure in the item stack is high, there is danger that two articles are pulled off at the same time as a result of the frictional force between the individual items. On the other hand, if the item stack is not compact enough, the throughput is relatively low. The individual items additionally can tip over, thereby worsening the pull-off behavior. For that reason, a certain stack pressure range must be maintained in the separating region.
A suction device is installed underneath perforated friction belts to achieve an increase in the frictional force between the first item and the friction belt for the separation system. Consequently, the stack pressure is up to now checked with sensing levers and position sensors, which switch the separating blade and the conveyor belt underneath and thus also the item feeding device on and off via a two-position control. The sensing levers here are located in the region where the items are suctioned out. The sensing levers are consequently actuated by an excessively high stack pressure as well as by items that are suctioned in. The operation for controlling the stack pressure thus is not defined clearly. Thus, suctioned-in postcards can stop the separating blade and the conveyor belt underneath via the sensing levers as soon as a gap forms in the stack of items in front of the pull-off location. After all the items in front of this gap have been separated, the feeding device must move the item stack at least by the amount of the gap in the direction of the pull-off point until further items can be separated. As a result, larger gaps form in the conveying section, following the separation, and these worsen the throughput. In those cases, there is also an increased tendency to pull off two items at the same time, owing to the briefly increased stack pressure.
A further disadvantage arises from the fact that the sensing levers are spring-weight-systems, which vibrate strongly during the separation by suction.